NEW YORK (Reuters Health) - A person's native climate might influence how his or her body goes about burning calories, according to a study published Monday.

People whose ancestors hail from chilly regions have gene adaptations that may allow their bodies to produce more heat while burning calories, an international team of researchers reports, while those with roots in warmer climates use calories more efficiently and produce scant excess heat.

Mitochondria, found in every cell, are responsible for producing energy and play a key role in regulating metabolism. The DNA in mitochondria is inherited maternally, and shows "striking differences" from one geographic region to another, Douglas C. Wallace from the University of California at Irvine and colleagues note. To investigate whether adaptation to different climates might explain this variation, the researchers analyzed gene sequences from the mitochondria of 104 people who represented all the known major types of mitochondrial DNA.

In the Proceedings of the National Academy of Sciences paper, Wallace and his team report that mitochondrial gene variants may confer advantages in some climates, but disadvantages in others.

For instance, arctic and sub-arctic native peoples had variants that programmed them to produce more heat, but put out less energy. Their bodies were thus more efficient at keeping them warm. Previous studies have shown that indigenous populations around the North and South Poles tend to have a higher resting metabolism.

Tropical and sub-tropical natives made more efficient use of energy, producing little heat.

The authors say the variants are evidence of natural selection at work--that genes evolved in response to environmental stresses.

But this adaptive response might not be beneficial when people native to one climate relocate to another climate, the authors say. "Given that mitochondrial DNA lineages are functionally different, it follows that the same variants that are advantageous in one climatic and dietary environment might be maladaptive when these individuals are placed in a different environment," they write.

Natives of cold regions are used to stoking their bodies with heat-producing high-calorie meals. That dietary habit might not serve them well if they move to a warmer region, and may play a role in causing disease, the authors say.

"Ancient regionally beneficial mitochondrial DNA variants could be contributing to modern bioenergetic disorders such as obesity, diabetes, hypertension, cardiovascular disease, and neurodegenerative diseases as people move to new regions and adopt new lifestyles," they write.

SOURCE: Proceedings of the National Academy of Sciences 2002;10.1073/pnas.0136972100.

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